Control scheme for operating cordless power tool based on battery temperature

ABSTRACT

A power tool is provided including a housing; an electric motor disposed within the housing; a power terminal arranged to received electric power form a battery pack; a power switch circuit disposed between the power terminal and the electric motor; and a controller configured to control a switching operation of the power switch circuit to regulate power being supplied from the power terminal to the electric motor. The controller is configured to receive a temperature signal indicative of a temperature of the battery pack, determine if the temperature of the battery pack is below a lower temperature threshold, and operate the switching operation of the power switch circuit in a normal mode of operation if the temperature of the battery pack is greater than or equal to the low temperature threshold and in a cold mode of operation if the temperature of the battery pack is below the low temperature threshold.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/354,361 filed Jun. 24, 2016, which is incorporated herein byreference in its entirety.

FIELD

This disclosure relates to power tools, and in particularly to cordlesspower tools operated by battery packs.

BACKGROUND

Cordless power tools provide many advantages to traditional corded powertools. In particular, cordless tools provide unmatched convenience andportability. An operator can use a cordless power tool anywhere andanytime, regardless of the availability of a power supply. In addition,cordless power tools provide increased safety and reliability becausethere is no cumbersome cord to maneuver around while working on the job,and no risk of accidently cutting a cord in a hazardous work area.

However, conventional cordless power tools still have theirdisadvantages. Typically, cordless power tools provide far less power ascompared to their corded counterparts. Today, operators desire powertools that provide the same benefits of convenience and portability,while also providing similar performance as corded power tools.

In cordless power tools operated via a battery pack, proper managementof the temperature of the battery pack is important. While high batterytemperature may damage the cells and presents a fire hazard, low batterytemperature increases the impedance of the battery cells. Such acondition causes the voltage of the cells to sag well below theirnominal voltage. What is needed is a mechanism that protect the batterypack in cold temperature conditions.

SUMMARY

According to an embodiment of the invention, a power tool is providedincluding a housing; an electric motor disposed within the housing; apower terminal arranged to received electric power form a battery pack;a power switch circuit disposed between the power terminal and theelectric motor; and a controller configured to control a switchingoperation of the power switch circuit to regulate power being suppliedfrom the power terminal to the electric motor. The controller isconfigured to receive a temperature signal indicative of a temperatureof the battery pack, determine if the temperature of the battery pack isbelow a lower temperature threshold, and operate the switching operationof the power switch circuit in a normal mode of operation if thetemperature of the battery pack is greater than or equal to the lowtemperature threshold and in a cold mode of operation if the temperatureof the battery pack is below the low temperature threshold.

According to an embodiment, the controller is configured to monitor arotational speed of the electric motor and control the switchingoperation of the power switch circuit in a closed-loop speed controlscheme in the normal mode of operation. In the in the closed-loopcontrol scheme, the controller controls the switching operation of thepower switch circuit based on the rotational speed of the motor. In anembodiment, the controller is configured to set a pulse-width modulation(PWM) duty cycle associated with the power switch circuit based on therotational speed of the motor in closed-loop speed control.

According to an embodiment, the control is configured to control theswitching operation of the power switch circuit in an open-loop speedcontrol scheme in the cold mode of operation. In the open-loop controlscheme, the controller controls the switching operation of the powerswitch circuit independently of the rotational speed of the motor.

According to an embodiment, at motor start-up, the controller sets atarget speed for the electric motor and control the switching operationof the power switch circuit to gradually increase a rotational speed ofthe motor from zero to the target speed at a ramp-up rate. In anembodiment, the controller is configured to set the ramp-up rate to afirst ramp-up rate in the normal mode of operation and to a secondramp-up rate that is smaller than the first ramp-up rate in the coldmode of operation.

According to an embodiment, the controller is configured to control apulse-width modulation (PWM) duty cycle associated with the power switchcircuit to control the rotational speed of the motor. The controllersets a target PWM duty cycle and increases the PWM duty cycle from zeroto the target PWM duty cycle at the first ramp-up rate in the normalmode of operation and at the second-ramp-up rate in the cold mode ofoperation.

According to an embodiment, the controller is configured to return fromthe cold mode of operation to the normal mode of operation if thetemperature of the battery pack is greater than or equal to a hightemperature threshold that is greater than the low temperaturethreshold.

According to another aspect/embodiment of the invention, a power tool isprovided including a housing; an electric motor disposed within thehousing; a power terminal arranged to received electric power form abattery pack; and a controller configured to receive a state-of-chargesignal associated with a voltage level of one or more battery cellswithin the battery pack and a temperature signal indicative of atemperature of the battery pack. The controller is configured todetermine if the voltage level is below an under-voltage threshold, andcut off supply of power from the battery terminal to the motor is thevoltage threshold is below the under-voltage threshold. The controlleris further configured to determine if the temperature of the batterypack is below a lower temperature threshold, and set the under-voltagethreshold to a first voltage threshold if the temperature of the batterypack is greater than or equal to the low temperature threshold and to asecond voltage threshold smaller than the first voltage threshold if thetemperature of the battery pack is below the low temperature threshold.

According to an embodiment, the controller is configured to reset theunder-voltage threshold from the second voltage threshold to the firstvoltage threshold if the temperature of the battery pack is greater thanor equal to a high temperature threshold that is greater than the lowtemperature threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of this disclosure in any way.

FIG. 1 depicts a perspective view of an exemplary power tool, accordingto an embodiment of the invention;

FIG. 2 depicts a size cross-sectional view of the exemplary power tool,according to an embodiment of the invention;

FIGS. 3 and 4 depict perspective exploded views of the exemplary powertool, according to an embodiment of the invention;

FIGS. 5A and 5B depict perspective views of a brushless DC (BLDC) motordisposed within the power tool, according to an embodiment of theinvention;

FIG. 6 depicts an exploded view of the BLDC motor, according to anembodiment of the invention;

FIG. 7 depicts an exploded view of a power module disposed adjacent themotor, according to an embodiment of the invention;

FIG. 8 depicts an exemplary circuit block diagram of a cordless powertool including a motor control circuit, according to an embodiment;

FIG. 9 depicts an exemplary circuit block diagram of a corded power toolincluding a motor control circuit, according to an embodiment;

FIG. 10 depicts an exemplary circuit diagram of an three-phase invertercircuit for driving a BLDC motor, according to an embodiment;

FIG. 11 depicts an exemplary waveform diagram of a pulse-widthmodulation (PWM) drive sequence of the three-phase inventor bridgecircuit of FIG. 10 within a full 360 degree conduction cycle, accordingto an embodiment;

FIG. 12 depicts a control unit for operating a BLDC motor, according toan additional and/or alternative embodiment of the invention;

FIG. 13 depicts an exemplary circuit diagram of a power supply regulatorincluding a leakage shutdown circuit, according to an embodiment;

FIG. 14 depicts a circuit diagram showing a solenoid switch used in aconventional corded power tool;

FIG. 15 depicts an exemplary circuit diagram of a cordless power toolincluding a controllable solenoid switch, according to an embodiment;and

FIG. 16 depicts an exemplary flow diagram for controlling a coldoperation and normal operation of the power tool, according to anembodiment.

DETAILED DESCRIPTION

The following description illustrates the claimed invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the disclosure, describes severalembodiments, adaptations, variations, alternatives, and uses of thedisclosure, including what is presently believed to be the best mode ofcarrying out the claimed invention. Additionally, it is to be understoodthat the disclosure is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. The disclosure iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

As shown in FIGS. 1-4, according to an embodiment of the invention, apower tool 10 is provided including a housing 12 having a gear case 14,a field case 16, a handle portion 18, and a battery receiver 20. FIG. 1provides a perspective view of the tool 10. FIG. 2 provides a side viewof tool 10 including its internal components. FIGS. 3 and 4 depict twoexploded views of tool 10. Power tool 10 as shown herein is an anglegrinder with the gear case 14 housing a gear set (not shown) that drivesa spindle 24 arranged to be coupled to a grinding or cutting disc (notshown) via a flange (or threaded nut) 25 and guarded by a disc guard 26.It should be understood, however, that the teachings of this disclosuremay apply to any other power tool including, but not limited to, a saw,drill, sander, and the like.

In an embodiment, the field case 16 attaches to a rear end of the gearcase 14 and houses a motor 28 operatively connected to the gear set 22.The handle portion 18 attaches to a rear end 30 of the field case 16 andincludes a trigger assembly 32 (also referred to as an actuator)operatively connected to a control module 11 disposed within the handleportion 18 for controlling the operation of the motor 28. The batteryreceiver 20 extends from a rear end 31 of the handle portion 18 fordetachable engagement with a battery pack (not shown) to provide powerto the motor 28. The control module 11 is electronically coupled to apower module 34 disposed substantially adjacent the motor 28. Thecontrol module 11 controls a switching operation of the power module 34to regulate a supply of power from the battery pack to the motor 28. Thecontrol module 11 uses the input from the trigger assembly 32 to controlthe switching operation of the power module 34. In an exemplaryembodiment, the battery pack may be a 60 volt max lithium-ion typebattery pack, although battery packs with other battery chemistries,shapes, voltage levels, etc. may be used in other embodiments.

In various embodiments, the battery receiver 20 and battery pack may bea sliding pack disclosed in U.S. Pat. No. 8,573,324, hereby incorporatedby reference. However, any suitable battery receiver and battery backconfiguration, such as a tower pack or a convertible 20V/60V batterypack as disclosed in U.S. patent application Ser. No. 14/715,258 filedMay 18, 2015, also incorporated by reference, can be used. The presentembodiment is disclosed as a cordless, battery-powered tool. However, inalternate embodiments power tool can be corded, AC-powered tools. Forinstance, in place of the battery receiver and battery pack, the powertool 10 include an AC power cord coupled to a transformer block tocondition and transform the AC power for use by the components of thepower tools. Power tool 10 may for example include a rectifier circuitadapted to generate a positive current waveform from the AC power line.An example of such a tool and circuit may be found in US PatentPublication No. 2015/0111480, filed Oct. 18, 2013, which is incorporatedherein by reference in its entirety.

Referring to FIG. 2, the trigger assembly 32 is a switch electricallyconnected to the control module 11 as discussed above. The triggerassembly 32 in this embodiment is an ON/OFF trigger switch pivotallyattached to the handle 18. The trigger 32 is biased away from the handle18 to an OFF position. The operator presses the trigger 32 towards thehandle to an ON position to initiate operation of the power tool 10. Invarious alternate embodiments, the trigger assembly 32 can be a variablespeed trigger switch allowing the operator to control the speed of themotor 28 at no-load, similar to variable-speed switch assembly disclosedin U.S. Pat. No. 8,573,324, hereby incorporated by reference. However,any suitable input means can be used including, but not limited to atouch sensor, a capacitive sensor, or a speed dial.

In an embodiment, power tool 10 described herein is high-power powertool configured to receive a 60V max battery pack or a 60V/20Vconvertible battery pack configured in its 60V high-voltage-rated state.The motor 28 is accordingly configured for a high-power application witha stator stack length of approximately 30 mm. Additionally, as laterdescribed in detail, the power module 34, including its associated heatsink, is located within the field case 16 in the vicinity of the motor28.

While embodiments depicted herein relate to a DC-powered power toolpowered by a battery pack, it is noted that the teachings of thisdisclosure also apply to an AC-powered tool, or an AC/DC power tool asdisclosed in WO2015/179318 filed May 18, 2015, which is incorporatedherein by reference in its entirety.

FIGS. 5A and 5B depict two perspective views of motor 28, according toan embodiment. FIG. 6 depicts an exploded view of the motor 28,according to an embodiment. As shown in these figures, the motor 28 is athree-phase brushless DC (BLDC) motor having a can or motor housing 29sized to receive a stator assembly 70 and a rotor assembly 72. Variousaspects and features of the motor 28 are described herein in detail. Itis noted that while motor 28 is illustratively shown in FIGS. 1-9 as apart of an angle grinder, motor 28 may be alternatively used in anypower tool or any other device or apparatus.

In an embodiment, rotor assembly 72 includes a rotor shaft 74, a rotorlamination stack 76 mounted on and rotatably attached to the rotor shaft74, a rear bearing 78 arranged to axially secure the rotor shaft 74 tothe motor housing 29, a sense magnet ring 324 attached to a distal endof the rotor shaft 74, and fan 37 also mounted on and rotatably attachedto the rotor shaft 74. In various implementations, the rotor laminationstack 76 can include a series of flat laminations attached together via,for example, an interlock mechanical, an adhesive, an overmold, etc.,that house or hold two or more permanent magnets (PMs) therein. Thepermanent magnets may be surface mounted on the outer surface of thelamination stack 76 or housed therein. The permanent magnets may be, forexample, a set of four PMs that magnetically engage with the statorassembly 70 during operation. Adjacent PMs have opposite polarities suchthat the four PMs have, for example, an N-S-N-S polar arrangement. Therotor shaft 74 is securely fixed inside the rotor lamination stack 76.Rear bearing 78 provide longitudinal support for the rotor 74 in abearing pocket (described later) of the motor housing 29.

In an embodiment, fan 37 of the rotor assembly 72 includes a back plate60 having a first side 62 facing the field case 16 and a second side 64facing the gear case 14. A plurality of blades 66 extend axiallyoutwardly from first side 62 of the back plate 60. Blades 64 rotate withthe rotor shaft 44 to generate an air flow as previously discussed. Whenmotor 28 is fully assembled, fan 37 is located at or outside an open endof the motor housing 28 with a baffle 330 arranged between the statorassembly 70 and the fan 37. The baffle 330 guides the flow of air fromthe blades 64 towards the exhaust vents 58.

FIG. 7 depict exploded views of the power module 34 adjacent the motor28, according to an embodiment. As shown herein, in an embodiment, powermodule 34 includes a power board 180, a thermal interface 182, and aheat sink 184 which attach to the rear end of the motor housing 29 viafasteners 191. Power module 34 may be further provided with a clamp ring190 that acts to clamp and cover the power board 180 and act as asecondary heat sink. Power module 34 may be disc-shaped to match thecylindrical profile of the motor 28. Additionally, power module 34 maydefine a center through-hole 192 that extends through the power board180 to accommodate the rotor shaft 44 in some embodiments. In anembodiment, through-holes 185, 187, and 189 similarly extend through theclamp ring 190, thermal interface 182, and heat sink 184, as furtherdescribed later.

In an embodiment, power board 180 is a generally disc-shaped printedcircuit board (PCB) with six power transistors 194, such as MOSFETsand/or IGTBs, that power the stator windings 86 of the motor 28, on afirst surface thereof. Power board 180 may additionally include othercircuitry such as the gate drivers, bootstrap circuit, and all othercomponents needed to drive the MOSFETs and/or IGTBs. In addition, powerboard 180 includes a series of positional sensors (e.g., Hall sensors,not shown) on a second surface thereof opposite the first surface, asexplained later in detail.

In an embodiment, power board 180 is electrically coupled to a powersource (e.g., a battery pack) via power lines 199 for supplying electricpower to the transistors 194. Power board 180 is also electricallycoupled to a controller (e.g., inside control unit 11 in FIG. 2) viacontrol terminal 193 to receive control signals for controlling theswitching operation of the transistors 194, as well as providepositional signals from the positional sensors 322 to the controller.The transistors 194 may be configured, for example, as a three-phasebridge driver circuit including three high-side and three low-sidetransistors connected to drive the three phases of the motor 28, withthe gates of the transistors 194 being driven by the control signalsfrom the control terminal 193. Examples of such a circuit may be foundin US Patent Publication No. 2013/0342144, which is incorporated hereinby reference in its entirety. In an embodiment, power board 180 includesslots 198 for receiving and electrically connecting to the inputterminals 104. In an embodiment, slots 198 may be defined and spreadaround an outer periphery of the power board 180. The outputs of thetransistors bridge driver circuit is coupled to the motor 28 phases viathese input terminals 104.

Referring to FIG. 8, a circuit block diagram of power tool 10 includinga motor 28 and a motor control circuit 204 is depicted, according to anembodiment. In an embodiment, motor control circuit 204 includes a powerunit 206 and a control unit 208. In FIG. 8, power tool 10 received DCpower from a DC power source such as a battery pack via B+ and B−terminals.

In an embodiment, power unit 206 may include a power switch circuit 226coupled between the power source B+/B− terminals and motor windings todrive BLDC motor 28. In an embodiment, power switch circuit 226 may be athree-phase bridge driver circuit including six controllablesemiconductor power devices (e.g. FETs, BJTs, IGBTs, etc.), such aspower devices 198 shown in FIG. 7.

In an embodiment, control unit 208 may include a controller 230, a gatedriver 232, a power supply regulator 234, and a power contact switch236. In an embodiment, controller 230 is a programmable device arrangedto control a switching operation of the power devices in power switchingcircuit 226. In an embodiment, controller 230 receives rotor rotationalposition signals from a set of position sensors 238 provided in closeproximity to the motor 28 rotor. In an embodiment, position sensors 238may be Hall sensors. It should be noted, however, that other types ofpositional sensors may be alternatively utilized. It should also benoted that controller 230 may be configured to calculate or detectrotational positional information relating to the motor 28 rotor withoutany positional sensors (in what is known in the art as sensorlessbrushless motor control). Controller 230 may also receive avariable-speed signal from variable-speed actuator or a speed-dial.Based on the rotor rotational position signals from the position sensors238 and the variable-speed signal, controller 230 outputs drive signalsUH, VH, WH, UL, VL, and WL through the gate driver 232, which provides avoltage level needed to drive the gates of the semiconductor switcheswithin the power switch circuit 226 in order to control a PWM switchingoperation of the power switch circuit 226.

In an embodiment, power supply regulator 234 may include one or morevoltage regulators to step down the power supply to a voltage levelcompatible for operating the controller 230 and/or the gate driver 232.In an embodiment, power supply regulator 234 may include a buckconverter and/or a linear regulator to reduce the power voltage of powersupply interface 128-5 down to, for example, 15V for powering the gatedriver 232, and down to, for example, 3.2V for powering the controller230.

In an embodiment, power contact switch 236 may be provided between thepower supply regulator 234 and the gate driver 232. Power contact switch236 may be an ON/OFF switch coupled to the ON/OFF trigger or thevariable-speed actuator to allow the user to begin operating the motor28, as discussed above. Power contact switch 236 in this embodimentdisables supply of power to the motor 28 by cutting power to the gatedrivers 232. It is noted, however, that power contact switch 236 may beprovided at a different location. In an alternative embodiment, powercontact switch 236 is provided within the power unit 206 between thebattery terminal (B+ and/or B−) and the power switch circuit 226. It isfurther noted that in an embodiment, power tool 128 may be providedwithout an ON/OFF switch 236, and the controller 230 may be configuredto activate the power devices in power switch circuit 226 when theON/OFF trigger (or variable-speed actuator) is actuated by the user.

FIG. 9 depicts a block circuit diagram of power tool 10 that receivedpowers from an AC power supply such as, for example, an AC powergenerator or the power grid. As the name implies, BLDC motors aredesigned to work with DC power. Thus, in an embodiment, power unit 206is provided with a rectifier circuit 220 between the power supply andthe power switch circuit 226. In an embodiment, power from the AC powerlines as designated by VAC and GND is passed through the rectifiercircuit 220 to convert or remove the negative half-cycles of the ACpower. In an embodiment, rectifier circuit 220 may include a full-wavebridge diode rectifier 222 to convert the negative half-cycles of the ACpower to positive half-cycles. Alternatively, in an embodiment,rectifier circuit 220 may include a half-wave rectifier to eliminate thehalf-cycles of the AC power. In an embodiment, rectifier circuit 220 mayfurther include a bus capacitor 224. In another embodiment, activerectification may be employed, e.g., for active power factor correction.In an embodiment, bus capacitor 224 may have a relatively small value toreduce voltage high-frequency transients on the AC power supply.

FIG. 10 depicts an exemplary power switch circuit 226 having athree-phase inverter bridge circuit, according to an embodiment. Asshown herein, the three-phase inverter bridge circuit includes threehigh-side FETs and three low-side FETs. The gates of the high-side FETsdriven via drive signals UH, VH, and WH, and the gates of the low-sideFETs are driven via drive signals UL, VL, and WL. In an embodiment, thedrains of the high-side FETs are coupled to the sources of the low-sideFETs to output power signals PU, PV, and PW for driving the BLDC motor28.

FIG. 11 depicts an exemplary waveform diagram of a pulse-widthmodulation (PWM) drive sequence of the three-phase inventor bridgecircuit of FIG. 10 within a full 360 degree conduction cycle. As shownin this figure, within a full 360° cycle, each of the drive signalsassociated with the high-side and low-side power switches is activatedduring a 120° conduction band (“CB”). In this manner, each associatedphase of the BLDC 202 motor is energized within a 120° CB by apulse-width modulated voltage waveform that is controlled by the controlunit 208 as a function of the desired motor 28 rotational speed. Foreach phase, the high-side switch is pulse-width modulated by the controlunit 208 within a 120° CB. During the CB of the high-side switch, thecorresponding low-side switch is kept low, but one of the other low-sideswitches is kept high to provide a current path between the power supplyand the motor windings. The control unit 208 controls the amount ofvoltage provided to the motor, and thus the speed of the motor, via PWMcontrol of the high-side switches.

It is noted that while the waveform diagram of FIG. 11 depicts oneexemplary PWM technique at 120° CB, other PWM methods may also beutilized. One such example is PWM control with synchronousrectification, in which the high-side and low-side switch drive signals(e.g., UH and UL) of each phase are PWM-controlled with synchronousrectification within the same 120° CB.

One aspect of the invention is described herein with reference to FIG.12.

FIG. 12 depicts control unit 208 of FIGS. 8 and 9 according to anadditional and/or alternative embodiment of the invention. As shownhere, the control unit 208 is provided, in addition or in place of powercontact switch 236, with a main solid-state switch 301 on the path ofthe Vcc power line from the power supply regulator 234 to the gatedrivers 232. Main switch 301 in this embodiment is a MOSFET, though itmust be understood that the main switch 301 may alternatively be an IGBTor any other solid-state switch capable of carrying sufficient currentto power the gate driver circuit 232. In this embodiment, main switch301 is a P-type switch. It must also be understood that main switch 301may be alternatively disposed at other locations within the power toolto cut off power from the power supply to the motor, e.g., between thepower supply regulator 234 and the controller 230.

In an embodiment, the gate of main switch 301 is controlled by thecontroller 230 via a secondary sold-state switch 302. Secondary switch302 is disposed between a ground signal (Gnd) and the gate of the mainswitch 301 and its gate is controlled via the controller 230. The gateof the main switch 301 is also coupled to the Vcc signal throughresistor 306. Under normal operating conditions, the gate of main switch301 is driven via the Gnd signal and kept ON. The resistor 306 allowsfor the Gnd signal to trump the Vcc signal and activate the main switch301. When a condition occurs that prompts the controller 230 to shutpower to the motor, the controller 230 deactivates the gate of thesecondary switch 302 via the VCC_SHUTDOWN signal, which is anactive-high signal. This in turn decouples the gate of the main switch301 from Gnd. The Vcc signal drives the gate of the main switch high,which turns off the main switch 301 and cuts off power from the powersupply regulator 234 to the gate driver 232. Such a condition mayinclude, but is not limited to, trigger release by the user, a batteryfault condition (e.g., over-current, over temperature, under-voltage), atool fault condition (e.g., over-temperature, over-current, stall,etc.), or a motor fault condition (e.g., over-speed, or incorrectrotation of the motor). The controller 230 may receive a fault signalfrom the battery pack (not shown) and initiate shut-down accordinglywhen a battery fault condition occurs. Additionally and/oralternatively, the controller 230 may monitor various tool, motor, orbattery operations and initiate shut-down on its own when it detects afault condition, and initiates tool shutdown via the secondary switch302.

As for motor fault conditions, in an embodiment, the controller 230 mayuse the hall signals Hall U, Hall V, and Hall W signals to determine therotational output speed and the direction of rotation of the motor. Inthe event the motor is rotating beyond a prescribed threshold speed(e.g., 30 k rpm for a grinder application), or in an incorrectdirection, the controller 230 may determine that there is a motor faultcondition. Upon detection of a motor fault condition, the controller 230initiates tool shut-down via the secondary switch 302.

According to an embodiment, the primary controller 230 may fail at timesfor various electro-mechanical or software reasons. Such failures mayinclude software bugs, contaminated routing and/or wiring, or a faultymicro-controller chip. It is thus important to protect users in theevent of a controller 230 failure, particularly from motor failures thatcan physically harm the user.

Accordingly, in an embodiment of the invention, an additional redundantcontroller 310 may be provided. Redundant controller 310 may be, forexample, a low cost, 8-bit micro-controller (such as a PIC10F200Microchip®) that is substantially smaller in size and more inexpensivethan the main controller 230. In an embodiment, redundant controller 310includes, in addition to power terminals Vdd+ and Vdd−, two inputterminals that receive two of the hall signals (in this case Hall U andHall V signals) and an output terminal that outputs a VCC_Shutdown_2signal. VCC_Shutdown_2 signal is an active-high signal coupled to a gateof a third solid-state switch 303, disposed in series with the secondaryswitch 302, as shown in FIG. 12. The redundant controller 310 determinesthe speed and rotational direction of the motor based on the two hallsignals. If the detected speed (as determined by the time gap betweenthe hall signals) exceeds a pre-programmed threshold, or if the sequenceof the signals is opposite a pre-programmed direction indicative of anincorrect rotational direction of the motor, the redundant controller230 deactivates the third switch 303 by disabling the VCC_Shutdown_2signal, which in turn turns off the main switch 301. This arrangementallows either the main controller 230 or the redundant controller 310 toshut off power to the motor in the event of a motor over-speed orincorrect rotation.

In this embodiment, the rotational direction of the motor ispre-programmed into the redundant controller. Such an arrangement issuitable for uni-directional tools such as a grinder. Alternatively, aredundant controller 230 may receive a desired rotation signal (e.g.,from a forward-reverse bar in a drill or an impact driver) and comparethe detected rotation to the desired rotation to determine if the motoris rotating in the correct direction.

Also, in this embodiment, the controller 230 and redundant controller310 monitor the rotational speed and/or direction of the motor 28 viaHall signals Hall_U, Hall_V, and Hall_W received from positional sensors238. It must be understood, however, that the teachings of thisdisclosure may apply to a sensorless brushless motor system, andcontroller 230 and redundant controller 310 may determine the speedand/or direction of the motor 28 via any sensorless speed control means,e.g., by monitoring a back electro-magnetic force (back-EMF) voltage ofthe motor, vector-space control, etc.

Another aspect of the invention is described herein with reference toFIG. 13 and with continued reference to FIG. 8.

Many of today's cordless power tools use lithium-ion battery packs topower the motor. An inherent characteristic of lithium-ion battery cellsis that they cannot recover or be recharged for reuse once they aredischarged below a minimum voltage threshold. For that reason, powertools and/or battery pack controls typically include a discharge controlmechanism to ensure that the lithium-ion cells of the battery pack arenot over-discharged. Such a discharge control typically monitors thestate of charge (e.g., cell voltage) of the battery pack cells and shutoff power supply from the battery pack in the event that the state ofcharge is below the minimum voltage threshold.

A problem arises when a battery pack is plugged into the power tool andthe power tool is in a “stuck trigger” condition. This condition occurswhen the tool trigger is inadvertently depressed (e.g., when placedagainst an object in a tool bag). Actuation of the trigger switchcreates a path for leakage current to discharge from the battery packeven when the tool is not in use. This leakage current continues topower the controller 230, and although the leakage current is relativelysmall, it can over-discharge the battery pack. The controller 230 isunable to disable the battery pack even when a battery under-voltagecondition is detected. A mechanism is needed to ensure that this “stucktrigger” condition does not over-discharge the battery pack.

For example, in FIG. 8, in a “stuck trigger” condition, power contactswitch 236 continues to power the controller 230 through the powersupply regulator 234, creating a leakage path for the battery pack. Aspreviously described, the power contact switch 236 may be disposedbetween power supply regulator 234 and the gate driver 232 and/or thecontroller 230. Alternatively, the power contact switch 236 may bedisposed between the battery terminal (B+ and/or B−) and the powerswitch circuit 226. This embodiment is described, by way of example,with respect to the latter arrangement of the power contact switch 236.

In order to ensure that inadvertent trigger depression does notover-discharge the battery pack, in an embodiment of the invention,power supply regulator 234 circuit, as described with reference to FIG.8, is additionally provided with a leakage shutdown circuit 235,described herein with reference to FIG. 13.

In an embodiment, the power supply regulator 234 includes one or morevoltage regulators (not shown) arranged to step down the voltage of thepower supply to produce the Vcc and Vdd voltage signals, which aresuitable for operating the controller 230 and/or the gate driver 232.Resistor R-Load in this circuit represents the load asserted by thevoltage regulators.

In an embodiment, the power supply regulator 234 includes B+ and B−terminals coupled respectively to the B+ and B− nodes of the batterypack. Power supply regulator 234 also includes a solid-state load switch402 provided between the B+ terminal and R-Load. When the load switch402 is off, the B+ terminal is cut off from the load R-Load, thusminimizing the leakage current being discharged from the battery pack.

In an embodiment, the power supply regulator 234 also includes aSW_Battery terminal, which is connected to the output of power contactswitch 236. In other words, power contact switch 236 is disposed on thecurrent path from the battery terminal B+ to both the power supplyregulator 234 and the power switch circuit 226. The power contact switch236 closes when the trigger switch (e.g., trigger 32 in FIG. 1) isactuated.

In an embodiment, an input voltage signal from the SW_Battery terminalis coupled to a gate of a control switch 404, which is in turn coupledto the gate of load switch 402. When the battery pack is plugged intothe tool 10 and the tool trigger switch 32 is actuated, the inputvoltage signal through the SW_Battery terminal activates the controlswitch 404. Activation of the control switch 404 grounds the gate of theload switch 402, which in this embodiment is a P-type solid state switchand is turned on when its gate is grounded. This occurrence connectsR-Load to the B+ terminal through diode D1, thus supplying power formthe battery pack to the load R-Load.

This connection powers up the controller 230. In an embodiment, thecontroller 230 is in turn configured to initiate a self-activatingfeedback signal Self_ON upon being powered ON. The Self_ON signalcontinues to keep the control switch 404, and thus the load switch 401,ON for as long as the controller 230 desires.

In an embodiment, controller 230 can also read the status of the triggerswitch (i.e., switch 420 and/or signal SW_Battery) through a logicsignal (herein represented by Trig_Logic). In an embodiment, theTrig_Logic signal is coupled in parallel with the C1 capacitor, acrossthe B− terminal and the output of the power contact switch 236, withinpower unit 206. Trigger_Logic signal is coupled to a node betweenresistors R2 and R3 disposed in series across the B− terminal and theoutput of the power contact switch 236. R2 and R3 resistors are sized toproduce a suitable voltage logic signal on the Trig_Logic signal whenpower contact switch 236 is closed.

In an embodiment, if the Trig-Logic signal is high for an extendedperiod of time (e.g., longer than 5 minutes), the controller 230 maydetermine a “stuck trigger” condition, i.e., that the trigger 32 hasbeen left depressed inadvertently. Absent the leakage shutdown circuit235 described in detail herein, the controller 230 in unable todeactivate the load switch 402 to cut off supply of power to R-Load, andthe controller 230 and/or gate driver 232 continue to place a load onthe battery pack.

To enable the controller 230 to shut down the load switch 402 while thetrigger switch 32 is still depressed, in an embodiment, the leakageshutdown circuit 235 is provided on the current path from the SW_Batteryterminal to gate of switch 404. The leakage shutdown circuit 235 isactivated via a self-deactivating Self_OFF signal from the controller230, and is operable to cut off the voltage signal from the SW_Batteryterminal.

In an embodiment, the leakage shutdown circuit 235 is provided with alogic-state override switch 408. In an embodiment, override switch 408is disposed between the SW_Battery and B− terminals, and is coupledtogether with the SW_Battery terminal to the gate of the control switch404. During normal operation, the override switch 408 is kept OFF. Whenswitch 408 is turned ON, it overrides the SW_Battery terminal signalthrough resister R4 and grounds the gate of control switch 404, which inturn disables load switch 402.

In an embodiment, when the controller 230 determines a “stuck trigger”condition, it initiates tool shutdown by deactivating the Self_ON signaland simultaneously activating the Self_OFF signal. The Self_OFF signalis coupled to the gate of the override switch 408, and thus disables thecontrol switch 404, and subsequently load switch 402, once thecontroller 230 determines a “struck trigger” condition.

Once the load switch 402 is turned OFF, it cuts power to the controller230. The Self_OFF signal can therefore be active for a very short periodof time. In order to prevent the SW_Battery terminal from reactivatingthe control switch 404 and load switch 402 after the controller 230loses power, the leakage shutdown circuit 235 is provided with a latchcircuit including a first switch 410 and a second switch 406. In anembodiment, the Self_OFF signal turns ON third switch 410, which isdisposed between the B− node and the gate of the second switch 406. Thesecond switch 406 is a P-type switch, and is therefore activated whenthe Self_OFF signal is high. The second switch 406 in turn couples theSW_Battery terminal to the gate of override switch 408 to keep overrideswitch 408 ON. The B+ power through the SW_Battery terminal continues tokeep override switch 408 ON even after the controller 230 loses powerand the Self_OFF signal is disabled. The battery B+ power line is alsocoupled to the gate of first switch 410 to create a latching circuit forthe gate of override switch 408 even after the Self_OFF signal isdisabled. In an embodiment, this latching mechanism continues to keepswitch 408 ON as long as the “stuck trigger” condition persists.

Another aspect of the invention is described herein with reference toFIGS. 14 and 15.

Use of a solenoid switch for AC power tools is well known. A solenoidswitch, as shown in FIG. 14, is made up on a spring-loaded power contactswitch, and a solenoid. When the user presses the power tool ON/OFFswitch against the force of the spring, it closes the switch. Thesolenoid is then energized via the electric power from the AC powersource, which then asserts a magnetic force on the contact switch tokeep the contact switch closed against the force of the spring.

A solenoid switch is typically used in AC power tools as a “no-volt”protection mechanism. A “no-volt” condition refers to a situation wherethe tool is plugged in while the power switch is in the ON position,which starts the motor immediately after the user has plugged it in.This is dangerous to the user and the work environment. By using asolenoid switch in place of a regular ON/OFF switch, the load of thespring pops the switch every time AC power is cut off from the tool.Thus, a no-volt condition is avoided the next time the tool is pluggedinto an AC power source.

PCT Application Publication No. WO 2015/179318 filed May 18, 2015describes various high power cordless DC and AC/DC power tools, such as60V or 120V power tools employing one or more 60V DC battery packs.These may include fixed-seed power tools such as cordless table saws,compressors, etc. that are conventionally corded AC tools. Instead of atrigger switch, such tools are typically provided with acurrent-carrying mechanical ON/OFF power switch that cuts off power fromthe power supply to the motor. The “no-volt” condition describes may bean issue in such tools where, for example, the battery pack (or batterypacks) are inserted into the tool while the power switch is in the ONposition. In addition, such tools should provide the controller theability to shut the tool down in the event of detection of a batterypack, tool, or motor fault condition previously described.

Thus, according to an embodiment of the invention, as shown in the blockdiagram 500 of FIG. 15 for a high power DC cordless power tool, aswitching arrangement 502 is provided on the DC bus line between thebattery terminals B+/B− and the power switch circuit 226. In anembodiment, the switching arrangement includes a solenoid switch havinga spring-loaded contact ON/OFF power switch 504 and a solenoid 506. Whenthe user presses the ON/OFF power switch against the force of thespring, it closes the switch, which couples the power source to the toolcircuitry. The solenoid 506, which is arranged across the B+ and B−terminals, is then energized and asserts a magnetic force on the powerswitch 504 to keep the power switch closed against the force of thespring. By using a solenoid switch in place of a regular ON/OFF switch,the load of the spring pops the power switch 504 every time the batterypack is removed from the power tool, regardless of whether the userindeed turns off the power switch 504. Thus, a no-volt condition isavoided the next time another battery pack is inserted into the toolbattery receptacle.

Additionally, according to an embodiment, a solid-state semiconductorswitch 508 is provided in series with the solenoid 506 across the B+ andB− terminals. The semiconductor switch 508 is controllable by thecontroller 230 via a control signal MC. The controller 230 maydeactivate the switch 508 via the MC signal upon detection of a faultcondition. Such conditions may include, but are not limited to, abattery fault (e.g., over-current, over temperature, under-voltage)condition, a tool fault (e.g., over-temperature, over-current, stall,etc.) condition, or a motor fault (e.g., over-speed, or incorrectrotation) condition. When switch 508 is deactivated by the controller230, it cuts off the solenoid 506 from the power supply, which in turnpops the power switch 504. Thus, in addition to no-volt protection bythe solenoid switch, the controller 230 can also de-energize thesolenoid to shut off the power switch 504 upon detection of any faultcondition.

Another aspect of the invention is described herein with reference toFIG. 16.

In a DC power tool operated via a battery pack, proper management of thetemperature of the battery pack is important. While high batterytemperature may damage the cells and presents a fire hazard, low batterytemperature increases the impedance of the battery cells. Such acondition causes the voltage of the cells to sag well below theirnominal voltage by 50% at full charge and by up to 75% at a lower stateof charge during tool start up.

During normal operation of the power tool, the controller 230 isconfigured to execute various tool and motor control algorithms thatoptimize the performance of the power tool.

For example, in an embodiment, during normal operation, the controller230 may be configured to monitor the state of charge of the battery packand shut off power from the battery pack in the event of a cell undervoltage condition (e.g., when the battery cell voltage falls to lessthan 2V/cell).

In an embodiment, during normal operation, the controller 230 may alsobe configured to execute a “soft-start” algorithm, where the pulse-widthmodulation (PWM) duty cycle of the motor drive signals is graduallyincreased from zero to a target PWM (e.g., at a rate of 0.2% every 1 ms)until the motor rotational speed reaches a target speed set. This targetspeed may be set to a predetermined value for fixed-speed tools, or maybe set in accordance to a trigger switch or a speed dial position forvariable-speed tools.

In an embodiment, during normal operation, the controller 230 may alsobe configured to execute closed-loop speed control for the rotationalspeed of the motor. Closed-loop speed control refers to a speed controlmechanism in which the rotational speed of the motor is set, not justbased on trigger or speed dial position, but also based on the actualrotational speed of the motor. In an embodiment, the controller 230 mayset a target speed based on the trigger or speed dial position,determine the actual rotational speed of the tool using the rotorpositional sensors, and adjust motor speed so that the actual rotationalspeed of the motor matches the target speed. Thus, as load is applied tothe tool, more power is supplied to the motor so as to maintainrelatively constant output speed. In an embodiment, the controller 230may do this by adjusting the PWM duty cycle. Additionally and/oralternatively, the controller 230 may adjust the conduction band and/orangle advance for each phase of the motor commutation.

When the battery pack is tool cold, the aforementioned batterymanagement and tool control operations may require substantially morecurrent that the battery pack can optimally handle due to the lowimpedance of the battery cells in cold temperatures. This adverselyaffects the life of the battery pack.

In order to optimize battery and motor performance while the batterypack is still cold, particularly during tool start up, according to anembodiment of the invention, the controller 230 is configured to performcertain battery management and tool control operations differently thanduring normal operation.

For example, in an embodiment, during “cold pack” mode of operation, thecontroller 230 may be configured to set a lower battery cellunder-voltage threshold (e.g., 1.2V/cell rather than the normal2V/cell). This prevents undesired battery shutdown while the batterypack is still cold.

Furthermore, in an embodiment, during cold pack operation, thecontroller 230 may be configured to set a soft-start ramp-up rate thatis lower than the ramp-up rate during the normal mode of operation. Forexample, instead of increasing the PWM ramp-up at a rate of 0.2% every 1ms, the controller 230 may increase the PWM ramp-up at a rate of 0.1%every 1 ms. This prevents heavy increases in current draw from thebattery pack while it is still cold.

Furthermore, in an embodiment, during cold operation, the controller 230may be configured to execute “open-loop” speed control, and initiate“closed-loop” control as described above during the normal mode ofoperation. In open-loop control, the controller sets a target PWM dutycycle in accordance with a trigger or speed dial position (forvariable-speed tools), or based on a predetermined value (forfixed-speed tools), but does not use a feedback signal from therotational speed of the motor to further adjust the motor commutation.This prevents heavy increases in current draw from the battery packwhile it is still cold.

FIG. 16 depicts an exemplary flow diagram 600 for the controller 230 toexecute “col operation” and “normal operation” as described above. In anembodiment, in this process 600, which starts at A, step 602, thecontroller 230 receives a battery pack temperature signal from thebattery pack at step 604. In an embodiment, this signal may be receiveddirectly from a thermistor within the battery pack. Then, at step 606,the controller 230 determines whether the pack temperature is lower thana lower temperature threshold (e.g., −5° C.). If yes, the controller 230sets a cold flag at step 608. Otherwise, the controller 230 determineswhether the pack temperature is above a higher temperature threshold(e.g., −2° C.). This hysteresis thresholding ensures that the controller230 does not toggle between normal mode and cold pack mode when thebattery pack temperature hovers around the threshold value. Thecontroller 230 proceeds to B, at step 614, and determines whether thecold flag has been set at step 616. If the cold flag has been set, thecontroller enters the “cold operation” mode as described above, at step618. Otherwise the controller 230 enters the normal mode of operation atstep 620. The aforementioned process continues at step 622.

Some of the techniques described herein may be implemented by one ormore computer programs executed by one or more processors residing, forexample on a power tool. The computer programs includeprocessor-executable instructions that are stored on a non-transitorytangible computer readable medium. The computer programs may alsoinclude stored data. Non-limiting examples of the non-transitorytangible computer readable medium are nonvolatile memory, magneticstorage, and optical storage.

Some portions of the above description present the techniques describedherein in terms of algorithms and symbolic representations of operationson information. These algorithmic descriptions and representations arethe means used by those skilled in the data processing arts to mosteffectively convey the substance of their work to others skilled in theart. These operations, while described functionally or logically, areunderstood to be implemented by computer programs. Furthermore, it hasalso proven convenient at times to refer to these arrangements ofoperations as modules or by functional names, without loss ofgenerality.

Unless specifically stated otherwise as apparent from the abovediscussion, it is appreciated that throughout the description,discussions utilizing terms such as “processing” or “computing” or“calculating” or “determining” or “displaying” or the like, refer to theaction and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system memories orregisters or other such information storage, transmission or displaydevices.

Certain aspects of the described techniques include process steps andinstructions described herein in the form of an algorithm. It should benoted that the described process steps and instructions could beembodied in software, firmware or hardware, and when embodied insoftware, could be downloaded to reside on and be operated fromdifferent platforms used by real time network operating systems.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

1. A power tool comprising: a housing; an electric motor disposed withinthe housing; a power terminal arranged to received electric power form abattery pack; a power switch circuit disposed between the power terminaland the electric motor; and a controller configured to control aswitching operation of the power switch circuit to regulate power beingsupplied from the power terminal to the electric motor, the controllerbeing further configured to receive a temperature signal indicative of atemperature of the battery pack, determine if the temperature of thebattery pack is below a lower temperature threshold, and operate theswitching operation of the power switch circuit in a normal mode ofoperation if the temperature of the battery pack is greater than orequal to the low temperature threshold and in a cold mode of operationif the temperature of the battery pack is below the low temperaturethreshold.
 2. The power tool of claim 1, wherein the controller isconfigured to monitor a rotational speed of the electric motor andcontrol the switching operation of the power switch circuit in aclosed-loop speed control scheme in the normal mode of operation,wherein in the in the closed-loop control scheme, the controller isconfigured to control the switching operation of the power switchcircuit based on the rotational speed of the motor.
 3. The power tool ofclaim 2, wherein the controller is configured to set a pulse-widthmodulation (PWM) duty cycle associated with the power switch circuitbased on the rotational speed of the motor in closed-loop speed control.4. The power tool of claim 2, wherein the control is configured tocontrol the switching operation of the power switch circuit in anopen-loop speed control scheme in the cold mode of operation, wherein inthe open-loop control scheme, the controller is configured to controlthe switching operation of the power switch circuit independently of therotational speed of the motor.
 5. The power tool of claim 1, wherein atmotor start-up, the controller is configured to set a target speed forthe electric motor and control the switching operation of the powerswitch circuit to gradually increase a rotational speed of the motorfrom zero to the target speed at a ramp-up rate.
 6. The power tool ofclaim 5, wherein the controller is configured to set the ramp-up rate toa first ramp-up rate in the normal mode of operation and to a secondramp-up rate that is smaller than the first ramp-up rate in the coldmode of operation.
 7. The power tool of claim 6, wherein the controlleris configured to control a pulse-width modulation (PWM) duty cycleassociated with the power switch circuit to control the rotational speedof the motor, the controller being configured to set a target PWM dutycycle and increase the PWM duty cycle from zero to the target PWM dutycycle at the first ramp-up rate in the normal mode of operation and atthe second-ramp-up rate in the cold mode of operation.
 8. The power toolof claim 1, wherein the controller is configured to return from the coldmode of operation to the normal mode of operation if the temperature ofthe battery pack is greater than or equal to a high temperaturethreshold that is greater than the low temperature threshold.
 9. A powertool comprising: a housing; an electric motor disposed within thehousing; a power terminal arranged to received electric power form abattery pack; and a controller configured to receive a state-of-chargesignal associated with a voltage level of one or more battery cellswithin the battery pack and a temperature signal indicative of atemperature of the battery pack, wherein the controller is furtherconfigured to: determine if the voltage level is below an under-voltagethreshold, and cut off supply of power from the battery terminal to themotor is the voltage threshold is below the under-voltage threshold, anddetermine if the temperature of the battery pack is below a lowertemperature threshold, and set the under-voltage threshold to a firstvoltage threshold if the temperature of the battery pack is greater thanor equal to the low temperature threshold and to a second voltagethreshold smaller than the first voltage threshold if the temperature ofthe battery pack is below the low temperature threshold.
 10. The powertool of claim 9, wherein the controller is configured to reset theunder-voltage threshold from the second voltage threshold to the firstvoltage threshold if the temperature of the battery pack is greater thanor equal to a high temperature threshold that is greater than the lowtemperature threshold.